Process for improving the workability of titanium alloys



Unit

OF TITANIUM ALLOYS The present inventitin rlatesto a reeess f'ee-iraiasw iiig the workability (deformability) of titanium alloys.

The liofworkifig'; fofexiimplejfth e' fer p oftitaiiiu'irfalloys,"roecfuire's rlati ely glfforces whicli iiic'i'ease as the temperature of workingincreases. For example, with increasing quantities of aluiffiiium d States Patent in such alloys the resistance to deformation increases to such an extent that very high working temperatures are required, as with lower temperatures they cannot be worked with the power available or tend to crack. For this reason, titanium alloys containing over 6% of Al could not be used upon a commercial scale.

Pure titanium is very strongly embrittled at room temperature by the presence of hydrogen therein and many titanium alloys are embrittled at room temperatures by the presence therein of only very small quantities of hydrogen. The embrittlement causes a lowered impact resistance.

While it was previously believed that hydrogen only has deleterious eflfects in titanium alloys, it was unexpectedly found according to the invention that the hot workability of titanium alloys is improved thereby. For example, when a titanium alloy, whose workability is to be improved so that, for example, it can be worked at lower temperatures without difliculty, is melted in the presence of hydrogen it takes up hydrogen and the resulting hydrogen containing alloy is much more easily but worked than the hydrogen free alloy. In order to obtain good mechanical properties in the hot worked product, it is generally necessary to remove the hydrogen therefrom after the hot working has been completed.

The quantity of hydrogen required to improve the hot workability of the titanium alloys depends upon the composition of the individual alloy. In general, however, the quantity required lies between 0.01 and 1% by weight. Alloys which are especially difiicult to work in general will only take up limited quantities of hydrogen and in such alloys as much hydrogen is incorporated therein as is soluble therein. Alloys which are easier to work often have a larger atfinity for hydrogen so that in such instances less hydrogen is incorporated therein to improve their hot workability than corresponds to its maximum solubility.

The provess according to the invention is especially well suited for titanium alloys which preponderantly contain alpha-titanium mixed crystals, whether in oriented or unoriented form. Aluminum, tin, indium, gallium, oxygen, nitrogen, carbon and other elements come into consideration as alpha-stabilizers. Increasing quantities of these elements cause a deterioration in the hot work ing properties of titanium alloys. The addition of hydrogen stabilizes the beta-phase of the titanium alloy at the hot working temperature and the hot working properties are improved thereby.

The process according to the invention is particularly advantageous for titanium alloys containing over 6% of aluminum which have been rendered workable at eleam me: He

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2" vgtemempsr'amres by theinEor pora'tion of hydrogen ri The" hydrogen "can be incorporated" in the mammarloys innumeroiis' ways; The siniple'stmethod is to melt ddvvr'rthe ititanium alloyin a"hydrogen"atn'iospher =.f. The hydrogen take up calfbeiri'creasdby the'useof super; atmospheric pressures: In View of the hydrogen itake'ri upby the a ieythe ressure aa area-saw the'st' g pressure." on the'otherhan'd'; itj'ca'n als'o"be' advantag ous to melt down the allo'yjright from "the 'start at suba'tiii pheric pressures and ifnece's'sa'ry supplementing the' 'hydreg'eu in the" gas chamber" abovei'the' alloy; is not necessary tdm'elt I the alloy in a pure"hydr en atmo'sp ere and, fo exam'l inrtgasfstich as argon}. I maintain "a uniform ands'tabl'e Hydro containing 25-;50% of hydrogen have pr ass stnqmrarpressa e nr currents-pf 1' o m li fififi psf P. by' It 'is' alstip6s'sible irflihcbriioft?'hydrbgeh inf lie titanium alloy or to increase its hydrogen co'ri'teititby" ing the workpiece in which the hydrogen is to be incorporated at temperatures below its melting point in hydrogen or a hydrogen containing inert gas. It has, for example, been found especially advantageous to heat workpieces whose surfaces have been freed of oxygen first to temperatures of about 900 C. in a hydrogen containing atmosphere and then to lower the temperature slowly.

The process according to the invention is illustrated by the following examples:

Example 1 A titanium alloy containing 8% of aluminum was melted down in an atmosphere of argon and 25% hydrogen at atmospheric pressure in an arc and then allowed to solidify again. The resulting alloy contained 0.061% of hydrogen. A sample thereof was forged at 950 C. with a single stroke of a 400 kg. forging hammer. A 65% deformation with only small surface cracks was attained. When a further sample was additionally heated to 900 C. in hydrogen and permitted to cool in the oven, the hydrogen content increased to 0.505%. Its deformability under the same conditions increased to 78% without crack formation.

After the deformation the hydrogen content of the forged samples was reduced to below 0.002% by heating to 1000 C. in high vacuum. A corresponding sample which did not contain hydrogen was destroyed by forging under the same conditions.

Example 2 A titanium alloy containing 13% of aluminum was treated with hydrogen as described in Example 1. When it was melted down it took up to 0.05% of hydrogen and at a 65 deformation it exhibited somewhat greater crack formation than the sample containing 8% of aluminum prepared under the same conditions. The alloy by additional heating in hydrogen took up 0.24% of hydrogen and the alloy was then able to be deformed 69% with only slight crack formation. In this instance again a sample of the alloy which did not contain hydrogen was totally destroyed when forged.

Example 3 A titanium alloy containing 8% of aluminum and 3% of indium which could not be hot worked was melted down in a hydrogen containing argon atmosphere and then heated in a hydrogen atmosphere to 900 C. to provide a 0.16% hydrogen content therein. This hydrogen containing alloy could then be forged well at Example 4 A sheet of a 10% Al 90% Ti alloy 6.5 mm. thick was heated at 900 C. under hydrogen until it had taken up 1% by weight of hydrogen. The resulting sheet could then be hot rolled at temperatures over 750 C. down to'a thickness of 0.8 mm. without even the smallest crack formation. Hot rolling of the same sheet but without incorporation of hydrogen therein was impossible under the same rolling conditions. Marked edge cracks occurred even in the first passes and these covered more than /3 of the width of the sheet when it only had been reduced to a thickness of 1.5 mm.

In the same manner, the incorporation of hydrogen in titanium alloys facilitates their deformation in an extnusion press. Intermediate anneals can be carried between the individual working operations without any substantial loss of the hydrogen incorporated in the alloys.

We claim:

1. In a process for hot working of titanium alloys, the steps which comprise incorporating 0.05% to 1% of hydrogen in such alloys and hot working such hydroge containing alloys.

2. In a process for hot working of titanium alloys which predominantly contain alpha-titanium mixed crystals, the steps which comprise incorporating 0.05% to 1% of hydrogen in such alloys and hot working such hydrogen containing alloys.

v 3. The process of claim 2 in which said titanium alloy contains over 6% of aluminum.

4. The process of claim 1 in which said alloy is melted down under a hydrogen containing atmosphere to incorporate the hydrogen therein.

5. The process of claim 1 in which said alloy is heated in a hydrogen containing atmosphere to incorporate the hydrogen therein. 7 I

6. The process of claim 1 in which said alloy is melted down under an atmosphere containing at least 25% of hydrogen to incorporate the hydrogen therein.

7. The process of claim 1 in which said alloy is heated in an atmosphere containing at least 25% of hydrogen to incorporate the hydrogen therein.

' References Cited in the file of this patent Handbook on Titanium, by Heinrich K. Adenstedt, pages 1 -3-9, August 1954, Wright Air Development Center. 

1. IN A PROCESS FOR HOT WORKING OF TITANIUM ALLOYS, THE STEPS WHICH COMPRISE INCORPORATING 0.05% TO 1* OF HYDROGEN IN SUCH ALLOYS AND HOT WORKING SUCH HYDROGEN CONTAINING ALLOYS. 